L-dopa as substrate for human duodenal catechol-O-methyltransferase and aromatic L-amino acid decarboxylase.
Catechol-O-methyltransferase (COMT) and aromatic L-amino acid decarboxylase (AADC) activities were determined in human gastrointestinal samples. L-dopa was used as the substrate and the reaction products 3-O-methyldopa (3OMD) and dopamine were separated by reversed phase HPLC and detected by electrochemical or UV detection. COMT activities varied between 40-350 pmol/mg/min and AADC activities between 100-3300 pmol/mg/min in different parts of the gastrointestinal tract. COMT inhibitors nitecapone (OR-462) and OR-611 effectively inhibited human gastrointestinal COMT activity in vitro, the IC50 values ranging from 10-20 nM and 5-75 nM, respectively. In vitro carbidopa inhibited AADC slightly more effectively than benserazide.
Schultz
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Orion Pharmaceutica, Research Center, Espoo, Finland.
D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000378:metabolism*; D002394:Catechol O-Methyltransferase / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004386:Duodenum / Q000201:enzymology*; D004563:Electrochemistry; D006801:Humans; D007980:Levodopa / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity
D007980:Levodopa; D002394:Catechol O-Methyltransferase; D001142:Aromatic-L-Amino-Acid Decarboxylases